Ship of Theseus (S. by Dorst & Abrams) discussion

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Ship of Theseus Paradox

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Lindsey (Lindsey1980) Wikipedia has a pretty good overview of the Ship of Theseus Paradox concept. I haven't finished the book yet but considering how much of the theme focuses on identity it is definitely important.

Lindsey (Lindsey1980) Another interpretation:

The "problem of change and identity" is generally explained with the story of the Ship of Theseus:
In ancient times, there was a ship, called the "Theseus" after its famous former owner. As the years wore on, the Theseus started getting weak and creaky. The old boards were removed, put into a warehouse, and replaced with new ones. Then, the masts started tottering, and soon they, too, were warehoused and replaced. And in this way, after fifty years, this ship now has all new boards, masts, and everything. The question then arises: Is the ship in the harbor, now called S2, the same ship as the ship that was in the harbor, fifty years ago (called S1, for convenience)? In other words, is S2 really the "Theseus"?
There is one answer which is a little too easy and quick. One might say: "No, of course not. The Theseus has changed a lot, so it's not the same ship. At the end of your life, you're not going to be the same person as you were, when you were a teenager. You're going to change a lot in the meantime." However, this is not quite answering the intended question. What is intended by the question is the sense of the word, "same", in which an old woman is the same person at the end of her life as she is, at the beginning of her life. Certainly, the word, "same", has such a sense. After all, one implicitly depends on it when one says, for example, "She has changed a lot". In order for someone to change a lot, there has to be one person who underwent the change. (One could perhaps reject that sense, saying that objects do not change over time.)
Going back to the definition of "change", an object changes with respect to a property if the object has that property at one time, and at a later time, the object does not have the property. What changes is the fact that the object has a particular property. The only way that that fact can change is if the object remains in existence. One can therefore think of a continuing object as the ground of change, or the arena where change occurs, as it were. To get back to the Theseus, the question is: Has the Theseus merely changed a lot, or is the Theseus gone, being replaced by a new ship?
One may say, "Sure, it's just a refurbished Theseus, greatly changed to be sure, but still the Theseus". If one thinks in this manner, then consider what happens when the story is extended further. Suppose someone buys all the planks, masts and whatever that is stored in the warehouse, and out of all of those materials, and absolutely no others, he builds a ship according to the same plans that were used to build the ship, christened "the Theseus". And this ship, called S3, is launched and sits on the other side of the harbor where S2 is. Is S3 the same as S1? In other words, is this recently constructed ship, the same ship as the ship originally called the "Theseus", considering that S3 was built out of the same materials, and according to the same plans as S1.
One could take this concept even further by not only the properties but also its subject matter of the "ship". What if instead the warehoused planks, masts, and other materials were used to build something completely different from a ship, like a house. (A concept explored by the artist Simon Starling, who turned a shed into a working boat and then back into a shed, winning him the 2005 Turner Prize.) The same materials and supplies are being used; yet they have taken on a new form. This relates to the concept of recreation vs. destruction.
Inevitably, the problem arises: How can one ever say that both S2 and S3 are the same ship as S1, the original Theseus? This is because if they were both the same as S1, then they would have to be the same as each other. This follows from transitivity, which states that if x = y and x = z, then y = z. With S2 and S3 being clearly different ships, sitting on opposite sides of the harbor, three choices present themselves:
S2 is the same ship as S1;
S3 is the same ship as S1; or
neither is the same ship as S1, and S1 has ceased to exist.
How does one then decide which is the correct answer in this case? It is difficult to tell. Whenever one makes an identity claim (i.e. a claim which states that two things are the same), one almost always uses two different descriptions. Sometimes, one may say, "x = x", like "I am I", but such claims are not particularly interesting or informative. The interesting identity claims are claims where two different descriptions are used for one and the same thing. As an example, take these two descriptions: "the Morning Star", and "the Evening Star". Sometimes, one can look in the sky just before dawn, and see a very bright point of light — that has been called "the Morning Star". And then also, one can look in the sky just after sunset, and see a very similar point — that has been called "the Evening Star". The Morning Star is, in fact, identical to the Evening Star — both are the planet Venus. As such, they are "two" things, only in description, but in actuality, are one and the same thing under two different descriptions.
It is a similar case with S1, S2, and S3, those being three different abbreviations, standing for the following descriptions:
"S1", referring to the ship which sat in the harbor fifty years ago, newly christened "the Theseus";
"S2", referring to the ship which sits in the harbor now, with the new planks; and
"S3", referring to the ship which sits in the harbor, recently constructed out of the old planks.
When one, therefore, asks a question like, "Is S2 the same as S1?", one can be understood to mean this: "Is the ship which sits in the harbor now, with the new planks, the same ship as the ship which sat in the harbor fifty years ago, newly christened "the Theseus"?" Do those two descriptions refer to the same thing, or do they not?
Philosophers are not interested in the "Ship of Theseus" problem per se, but to a more basic problem which is this: How does one decide that X is the same as Y, where X describes something at one time, and Y describes another thing at a later time? This is called the "problem of identity over time", or alternatively, the "problem of change".

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Ship of Theseus (S. by Dorst & Abrams)

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